In this specification, a medium to read/write information such as an optical disk is referred to as an information recording medium. Conventionally, optical disks exist in which a phase change film is used for the recording layer such as a DVD-RAM, and an organic material is used for the information layer such as a CD-R and DVD-R. An optical disk using an organic material as the information layer has an information layer including a pigment, which has absorption in the wavelength of the recording light source, and recording is performed by changing the characteristics of the substrate surface connected thereto using laser irradiation.
As described in, for instance, patent document 1 (JP-A No. 122032/1983), a field-effect optical disk is well known, in which information is recorded on a phase change recording film by irradiating a laser beam under the condition where an electric field is applied to the recording layer. It is used for an element structure sandwiching a phase change information layer such as GeSbTe system between the upper and lower electrodes. It aims to accelerate the phase change (crystallization) by applying an electric field to the recording film than by only irradiating a laser beam.
Making multi-layers is well known as a method to increase the storage capacity of an optical disk using a phase change film. Patent document 2 (JP-A No. 30878/2004: US2004/0001418A1) discloses a two-layer type optical recording medium in which two recording layers consisting of a phase change material are laminated.
The inventors proposed an optical recording medium in non-patent document 1 (Proceedings SPIE vol. 5069, p. 300), in which more recording layers can be laminated by reversibly coloring the laminated recording layer using the principle of electrochromism.
Moreover, patent document 3 (JP-A No. 82360/2002) discloses an invention of a display device in which the principle of electrochromism is used. Furthermore, patent document 4 (JP-A No. 185288/1999) discloses an invention of an optical device recording information by coloring the reflection layer using electrochromism. Patent document 5 (JP-A No. 346378/2003: US2003/218941A1) discloses an invention of an information recording medium, in which information recording is carried out by applying a voltage to the upper and lower sides of the recording layer colored by electrochromism.    [Patent document 1] JP-A No. 122032/1983    [Patent document 2] JP-A No. 30878/2004    [Patent document 3] JP-A No. 82360/2002    [Patent document 4] JP-A No. 185288/1999    [Patent document 5] JP-A No. 346378/2003    [Non-patent document 1] Proceedings SPIE vol. 5069, p 300    [Non-patent document 2]    http://www.sanyovac.co.jp/Englishweb/products/EITOonglass.html    [Non-patent document 3] J. C. Street et. al. Physical Review B, Vol. 28, No. 4, p. 2140-2145